Output converters for digital computers



Sept. 19, 1961 R, J. FROGGATT ETAL 3,000,562

I OUTPUT CONVERTERS FOR DIGITAL COMPUTERS Filed Sept. 12, 1957 3 Sheets-Sheet 1 PIC-3.1

llrw (Elli 0E5 B J, Fr 0 @523 Sept. 19, 1961 R. J. FROGGATT ETAL 3,000,562

OUTPUT CONVERTERS FOR DIGITAL COMPUTERS Filed Sept. 12, 1957 s Sheets-Sheet :5

FIG. 3

11121) (ZZZ/2:036 liefFroyyaw .DJEI buzz/(saw United States Patent O This invention relates to output converters for computers.

In some output converters -for digital computers where an output from an intermediate section or final section of a computing machine, is presented as a number coded in serial binary form it is required to reconvert the digital coded number to a particular scale of units. For example,

if data representing sterling, pounds, shillings and pence,

is fed into the machine it' may be required of the machine to provide an answer in binary words representing each character on a sterling scale, suitable for printing out. A usual form for printing out may be on punched cards.

One type of output converter comprises essentially a store, preferably a magnetic drum store, on which are stored in binary digital form, equivalents on one or more scales, for example sterling or binary decimal scales and means for reading ofi these equivalents serially in response to the presence of digits 1 in a serial binary coded number presented to the converter. Clearly, adding means must be provided for the successive binary equivalents and difiiculty may be encountered in pro viding carries in this type of addition, since it is usually necessary to add fillers to each character of an equivalent when a carry is required. The nature of the fillers will be apparent from the following description of the invention.

Theobject of the present inventio n is toprovide iinproved'meansfor instrumenting carries -in output converters'.

According to the present invention there is provided digital conversion apparatus comprising a first store 'for signals representing a serial binary number to be con-" verted to another scale of notation, a second'store for equivalents in said other scale of possible bits insaid serial binary number'added 'toeach of which-are appropriate fillers according to said other scale of notation, gating means responsive to signals derived from said 'fir'st store'for selectively deriving signals representing corresponding equivalents'an'd tillers from said second store, serialbinary adding means for adding said signalsv to previously converted signals stored in a third store and means for'selectively subtracting'said fillers in the dependence upon thev occurrence of carries in predete'n. mined positions in theresultant produced by said adding means i In order that the invention may be clearly understood and re'adilycarried into: effect, the invention will be dc scribed-with referenceto the accompanying drawings, in which: f. I

FIGURE 1 illustrates diagrammatically and mainly in block form, one example Oran outputconverter according to the'invention,

FIGURE 2 illustrates simian sad in FIGURE 1 a;

units in order to simplify Referring to-FIGURE 2, symbol (4 denotes a pulse Patented Sept. 19, 1961 "ice connection a3. The figure enclosed in the symbol denotes the threshold of the gate, the figure being 2 in the example illustrated, thereby indicating that it would require the simultaneous application of pulses to twoinput connections to produce the single output pulse; A suitable form of pulse gate is described in the Proceedings of the I.R.E., May 1950, page 511.

Symbol (b) denotes a pulse inhibitor gate having a normal input connection b1, an inhibit input connection b2 and an output connection b3. A pulse applied to b2 inhibits the transmission of pulses from b1 to b3. A

. pulse. inhibitor gate may be of similar construction to a pulse gate. suchas represented by (a), with however, one of the controls reversed.

Symbol (c) denotes a two state device having an input connection 01, and output connection C2 and an inhibitor connection C3. When the device is in one state, the state 0, a signal on the connection C1 changes the device to the state 1, the device remaining in that state until a signal is applied to the inhibitor connection C3 whereupon the device reverts to state 0. In

. state 1 of the device, the output connection C2 is energised. A two-state device such as indicated by symbol (0) can be realised by means of an Eccles-Jordan circuit.

Symbol (d)denotes a delay element, manytorms of which are known in the art.

Symbol (e) denotes an end-of-pulse gate which produces a short pulse on an output connection e2 at the end of a pulse applied to the input connection e1. An end-ofpulse gate may consist for example, of a difierentiating circuit followed by a diode limiter to remove one of the pulses produced on differentiating the input.

The theory of the use of fillers is described in detail in an article entitled Serial digital adders for a variable radix ofnotation, page 410, Electronic Engineering October 1953. However the principle may be understood from the following considerations, in which reference will be made to FIGURE 1 which is to be described in greater detail after a picture of its required function has been presented. The circulation store 1 contains a series of 36 bits in increasing order of signals, the bit of highest significance representing sign. The drum store 3 carries equivalents of successive possible bits stored in 1. Each equivalent is made up of twelve characters each made up of six bits so that since the machine is synchronized throughout to operate in a bit by bit manner, a period of two complete cycles of the store 1, that is 72 bit periods, are ordinarily required to read out from the drum store an equivalent of a single bit in the store 1. Let it be assumed that the required conversion is from binary to binary decimal, that is each bit in the store 1 is to be examined successively and converted into twelve six bit decimal characters, these characters are fed successively bit by bit into an adding unit (which in FIGURE 1 is 13) to be added to previous conversion held in a circulating store 14. Y

The circulating store is capable of storing a complete conversion of the serial binary word stored in 1. Let it also be assumed for simplicity that a bit in the eighth bit place, in the store 1, is to be converted into binary decimal notation form namely 128. And, suppose further that 127-is held in the output store 14 by virtue of gate having inputconnections c1 and a; and. an output previous conversions, the required number to be stored in 14 is therefore 127+128=255 which if six-bit characters are used in binary decimal form is 2 scale of notation is vpends .uponthe cyclic period. forthe store. digitaloutput fromthe store, is fedinto a gatinggdevice the y sui a e ts h approp ate filler .0 sl fierem 3 adder 13, the-following is obtained on addition the first pair of characters namely 7 and 8:

and ordinarily this is what wouldbe fed to the store 14 for the-addition in that. particular vcharacter position. But 7+8=l5 ,so that what is required on thebinary decimal V 11,060161 I the digitof highest significance, *1 representing a carry from this character'position to the next. In order to r 'produc'e'this it'is necessary at some stage to introduce an additional quantity, namely 1",000 000010l0 or 110110 and this quantity-it known as the filler. This quantity :must only be added moreover when acarryis requiredand inorderto achieve 'this in the arrangement of FIGURE 1, to each character of the {equivalents stored in 3, Whether they be Zeroornota filler is added andiffno, carryifrom one character to'the nextisprbduced the appropriate filler is subtractedby theserial subtraction unit 23. Since the criteria for requirement ofa-filler are identicahfor each character on the binarydecimaliscale the filler which is" added to each-character isthesame, namely 110110. "There is ofcoursea possi bility of six carriesoccurring within aparticulat charactor but only'thecarry of-highestsignificance must be selected as-a criterion to determine-whetherthe filler must be removed or not from the particular character in: question. 'In order to provide-for this the carry-signal is gated out every sixth bit and a delay "of six digits is providedbetweenthe serial adding circuit -=13 and the serialsubtractioncircuit 23.to enable subtraction 'ofthe filler to-be inhibitedif a carry signal is present. The

filler for subtractionpu'rposesis storedin a circulating store. a I

In the case'of. other scales'of notationto which conversion may be'required, such for example-as sterling, different fillers namely 52 and I 44 are required in the production of the respective carriesifrorn pence :to shillings, and shillings tOcPOUHdS-bllt binary decimal .fillers again operate, of course tor the successive characters representing pounds.

which as mentionedabove denotes a circulating store which carries a=serial binary-coded number .which .it. is

required to convert into a forrnsuitable for. printing-out.

The word? stored in.1 consists of thirtyesix bits, one of these bits, in this .case the bit of greatest significance,. is usedto representthe sign of the .quantitystored. A, bit 1. represents.- aunegative sign. and a bit 0 represents. a positive sign. The thirty-six bits appear serially. at the output terminal of the store with a frequency which dewhich for simplicity isrepresentedibyvtheeblockl butis described in detail hereafterwith reierenceto FIGURES 3 and 4. Moreoverblock 2,also.containsacomplementer which is: responsiveto a signal indicating; a negative sign.

Further. circuit means. isalso provided in (2 which provides that in the event of a bit position in the store ,1 to be read; outyielding a signal representing an ,0 a -pulse' is providedin the, output {lead 26,as a result of read out; at that digit position. ,,The purpose of thispulseiwill become clear hereaften, Reference 3 as mentioned above cl'e; notes a. magnetic. drum store UPQn' ,Which .aIe,st0-red groups; of seventy-two bits,.each.groupjcomprising twelve six-bit characters representing numbersnon sterling. and

ter stored in 3. an appropriate fillenis ,added. Ehese quantities are storedon tracks 4 and 5 respectively but clearly if required further trac'ks-rrlay be included to carry scales of conversion. 'As' "will become l oi the firstithreebits stored in the'f not 'necess tr an 'are an astute; Mammar track Referring to =FIGURE1, reference 1.is .arectangle,

The .serial 6 which operates in conjunction with the gating devices 2 and whose purpose is the selection of successive digits from the store 1, being more fully described with reference to'FIGURE 3, is also provided on the drum. The a drum is driven by motor 24. The respective stor. age tracks are read by readers 7, 8 and 9, whose outputs are communicated via the pulsegate .10, inhibitor gate ceives an input pulse whence 16 is set toits energised state. The purpose ofthe gate l3ais to prevent other carries than are in the sixth digit position in eachcharacter irom producing a pulse at the input of 16. The output of 16 is connected viaa delay element 17 to its own inhibitor connection and also to the inhibitor connection of the gate 18. The input of 18 is connected to electronic switcheswhich are threshold 2 gates such as mentioned above, denoted by rectangles 19, 20, 21 which are instrumental in response to timing pulses from the conventional clock pulse device 22, to provide in binary coded form quantities equal .to the required fillers.

Fillers 54, 44 and 52 are indicated-being appropriate to pounds, shillings and pence respectively; the filler 54 being 1 used for binary decimal conversion.v I These are stored in circulating storesdenoted} by the respective blocks in thefigureb The output of 18 is connected to the negative input of a subtracting unit23 which derives itspositive input from the delay output of 15 and the difference output of 23 is connected back toithe accumu- Synchronism 7 between the store 1 the motor 24 which drives the drum 7 lator 14.where it continuesnt o circulate.

store .andthe accumulator 14 is provided connections to 22. I

by clock pulse ReferringjtoFIGURE 3, which illustrates in detail the v form and operation .of the gating devicewzof FIGURE 1 those components which are identical with those of FIG- URE 1' have the same references. The output of the circulatingstore is connected to one input connection for the pulse gate and to the normal input of the pulse inhibitor gate .31 .whose output is connected via the complementer 4110a further inhibitor gate 33 and .tonaninput of the 7 pulse gate 3'4. A suitable form of complementerjwould.

consist of an inhibit gate operated inresponse to the output of register 1 so that 07s and 1s areinterchanged,

followed. by an adder such as shown in Calculating Instruments and Machines by D. R. Hartry on pages. 10.0 and 104. The outputs from the drum readers .7 and 8, are communicatedvia pulse gate 10 and the inhibitor .gate 11 to. -afurther pulse gate 36. The output from :35 con stitutes the normal input fora twoestate device 37 the output of which is connected to an fend-of-pulse gate 38.

binary=decimal scalesrespectiycly,- andto; each charac I,

The inhibitor connection for 37 receives clock pulses at the. beginning of .each minor cycle. forms the-normal input for a further two-statedevice 39. Theiinhibitor connection for 39 is connected'via a suitable delay device 40 to its output which constitutes the other inputfor the pulse gate 36.- Thedevice lfl has =a-delay of 72 bit periods since inthis cas'e,each equivalent stored on the drum store 3 is composed ofi-twelve six-bit characters. The output 'of36 passes along with the output-of 3.4 toithe adder-'13. i It will be considered that one complete cycle 'of the store-1 constitutes a minor cycle two minorcycles -being required for conversion for-each bit'in this store and synchronism between-:1 and 24 fbeing provided in known manner clock pulsesfrom the clock- 22. The clock also providesclockpulses in leads 45f46Q47r-48, 49

and- 50. ""A' clock-pulse is appliedin' ls 'at the-thirty sixth The output of 38 a some? bitof the first minor cycle of a conversion and an inhibit input is present for-31. in 46 throughout the first minor cycle. An. inhibitor pulse is also applied to 47 at the finish of each conversion and to 48 at the commencement of each minor cycle. The lead 49 carries an inhibitor potential during the whole of the second minor cycle of a conversion and 50 carries a gating potential during the first three bit periods of the second minor cycle. These clock signals are indicated on the respective leads in FIG- URE 3, M.C. with suflix indicating which minor cycle is concerned and P with its sufiix indicating the periods of that minor cycle. V r V H In FIGURE 4, the fragment of the drum store shown extends over the stored equivalents. of two serial binary digits indicated as 2 and 2.. It is assumed that two alternative scales for the equivalents are given, binary decimal B D.) or sterling (S), The track indicated by (A) is the above-mentioned auxiliary track. The drum passes in the direction of the arrowv and the equivalents are read ofi by the reader 7v and the bits stored on the de-energised in readiness'for auxiliary track are read non-destru'ctively 011 by the reader 9. Each equivalent comprises a possible twelve characters composedof six bits each. This equivalent therefore to two words for each equivalent, each word comprising thirty-six bits or one minor cycle. On the auxiliary track, corresponding to bits comprising the first word of each equivalent, are stored thirty-six Os but corresponding to the second word of each equivalent a single 1 is stored, the position of the 1? in this word corre spending to the position of the next bit in the circulating store to be converted. Hence on the second word of the portion of the auxiliary track which corresponds to the equivalent of 2 a 1 is stored in the (n+'1)th bit position to correspondto the equivalent of 2 which is next to be read off. In the second word of the next portion shown of the auxiliary track a 1 is stored in the (n+2)th bit position as shown andso on. e

In operation of FIGURE 3, a'choice of binary-decimal or sterling conversion is made and if sterling is chosen a 1 potential is applied to in a suitable manner so that read-0E is from track 4. If binary-decimal is chosen no potential is applied in 25 and read-01f is then from 5. Clearly the switching potentials for 10 and 11 may be provided in any suitable known manner for example by means of a two position selector switch connectedto a source of gate potentials. During the first minor cycle of a conversion, the inhibitor signal in 46 for 31, is effective, and as input 45 of carries a gate pulse at the 36th digit, if the other input of 30 receives a 1 from the'circulating store, a negative sign for the conversion is indicated and the bistable device 42 is triggered to implement the complementer 41. e If 30 receives an 0 which represents a positive sign, the complementer is not implemented but simply forms a straight through path between its input and output. 'In the first minor cycle an indication is also communicated to the output printer for one is provided in the machine of the sign of the quantity about to be read out. During the second minor cycle 33 is inhibited whereas 31 is not, so that the output of circulating store 1 is communicated to one input of 34. The second input 50 of 34 carries inputs during the first three bit periods of this cycle sothat these bits are communicated directly via the complementer to the printer. No conversion is required for the three hits of lowest significance as they carry equal weight either on sterling or binary-decimal scales.

During the next two minor cycles the third and fourth minor cycles, no corresponding equivalents are stored on the drum but a 1 on the auxiliary track coincides in time with the fourth bit location in the circulating store. If the fourth bit is a lfa pulse output is produced by 35 which energises 37. The potential at the output of 37 now continues for :a period of thirty-two bit periods before being inhibited by a clock pulse. The end of pulse gate 38 then passes a pulse and the bistable element 39 is energised, the time at this instant corresponding to the beginning of the readoutfrom the first of the stored equivalents (i.e. 2 Thus bitsstored on the chosen equivalents track are transferred via the gate 36 to 13. At the end of 72 bit periods, 39 is de-energisedby the output of 40' but during the read out of this equivalent a .l is Ireadfrom the auxiliary track to correspond in position in the second word of this equivalent with the bit location of 2 to which the next equivalent which is to be read out corresponds. If the 2 or the fifth bit location is occupied by a l the gate 30 passes a pulse and the equivalent is read out. If an -0 is stored in the fifth bit location however, no read out occurs. This process continues to the end'of the word stored in 1 whereupon an inhibitor pulse is provided by 22 in 48 and 42 is the conversion of a new serial binarywordin 1;: a a

In operation of the arrangement of FIGURE 1,- during thefirst minor cycle; .that is'the first cycle of the storel, by means of the device 2, the bit of greatest significance is read out to'give the sign of the stored quantity and if a negative sign is recorded, the complementer is implemented and an indication that the quantity is negative sent to the printer which for simplicity is not indicated in the drawing since it forms no part of the invention. During the second minor cycle, the three bits of lowest significance as they have equal significance on either scale are transferred after complementing if required, directly to 13 and are therefore stored in 14.

' Assuming the conversion is to sterling, a potential is applied to the point 25, so that read-out from the drum store is from the track 4 andis effected by 7. In addition,

a setting is made in 22 to indicate that the conversion is sterling, in order that correct signals are applied by 22 to the switching units 19, 20 and 21. If the conversion is to decimal scale, no potential is applied to 25 so that read out is from the track 5 by reader 8.

Since there are seventy-two bits in each equivalent and thirty-six digits in the store 1, a period of two minor cycles is required for each equivalent to be read out. Considering subsequent minor cycles, in the minor cycle immediately previous to a pair of minor cycles constituting a particular equivalent, a 1 on the track 6 is read out in time coincidence with the position in 1 of the bit about to be converted. If this bit location carries a 1 it is instrumented by 2 that the equivalent is passed serially to 13 where it is added to the already accumulated quantity circulating in 14 and after a delay of 6 bit periods or one character period in 15, appears at one input to 23 If in the addition process no carry has occurred in 13, the appropriate filler is substracted in 23, but if how-' ever a carry has occurred it is indicated by an input to 16 from 13 so that the filler is inhibited by the gate 18 for that particular six digit word and no filler is subtracted in 23. If furthermore the bit location to be converted carries zero a pulse is applied in the lead 26 to 16 and the subtraction of the filler is again inhibited. There is clearly a possibility of eleven carries within the 12-character the period of read out of a single eqivalent. As an illustrative example of the invention let it be assumed that a word stored in 1 is required to be converted to binary decimal form and that the word represents a number 123 thus the word stored in 1 is In the first minor cycle of the conversion the gate 31 is inhibited and the gate 30 is opened for the 36th bit location which in this case has a 1, so that the complementer is not implemented and remains so until the end of the conversion. As the store 1 commences a fresh minor cycle gates 31, 33 and 34 are opened and 30 is closed, 34 remains open for the period of the first three bits of the word stored in 1 that is and therefore these bits are transferred directly to 13. Gate 34 then closes and 35 is not open during this minor cycle because and uring thel' suceeedin g eight minor eyeles ed mqrf Yer lgecapse s. n'pyv appear fA ltigepgh the abevedesjcri gibnjbf the invention has" been made with reference t6'seria1'binary'to binary deciinal gon'ver sion elearly the eirc uit in-FIGURE 1 is operjabie fiir sterling c'omier sidn where 'the serial binary n'u'm- Eel feibresntsbneep The respective fillers required are indicated'in the rectangles representing six bit circulating registers associated with't he selebtor switches 19, and

z; 'Ihejseswiteiies are selected byfsigfials fr m the black 111111122. i

- Ithpilgh moreqver the present embodiment Of the 'invein n'fhas been described in the fo r'egbing employing ei'realanng registers, thefinve'nt'ion is not li'rhited'tb cir-- euiating registers since the invention may readily be adapted by persbn s-skilledlin the art to use with other types of stprage device such for example as a' ma'gnetic core matrixstbrle In the ease of a magnetic core'matrix stdrimnaeans ,wqnl d felf example be prdvidedffor reading qu t sueeessive ibw's bfbitsinto a tefnporaryfirgis'ter and ther fter ig ati n g theindividual digits out to the gates in 3. any other 'alternative arrangementsan hdWeYer be devised using'th'e present inventidnt l Ait hol'lg h furthetlilorethe invention is dsc'r'ibed'with equit' a ms to sue'cessive bits in lec'atioiis in 'the store 1 s'tpr'eil alqn'gwuh the appropriate fillers on a magnetic dlfitin stare, the inv entidnis 'ndt limited "to theme of a drum s't 're. CIeaflY, sifnil'arlj to above, the drum 'store may lsub stitlited with anynther suitable type of stqre sueh-forfeXample asfa-n iagheti'c 'eo'i'e matrix store. 'wna u ami A'pparatus fer enniiei ting a serial binary cdded iginnibel gintqanother scale ef notation in whieh characters 4. arrangement aeeemmgw claim ilfsa id 'sjecbnd' store cdmprising anlag'fietic dilltm s'tbre, said 'stdr'e c mprising an auxiliary track whereon there are stored gating signals to eqincic le with regard to time of reading: out with the hit in said first eer e fthe eqiiiv'aientjbf 'Whibh 'is ne'xttqbe'fead ou Reieren'cesfiited iii-thefile of this patent UNITED 'STATES'PATENTS' V 'K Q GNE I N r at Britain Mar. 7, Q1956 OTHER REFERENCES Bird: Cqmpnting Maehi nes; Input jahd Ontput, -E1ectronie Engineering Octcybe'rf 1953) (pp. 407 to 410).

Townsend: Serial Digital Adders fer a VariableRadix bf Notation, 'El eetioiiic En i feermg (Octqbe'r 3) are expressedi11'binary coile, comprising a first register (ppfitl'd to 41 6).

Womersleyet a1. ,Aug. 4, 51 959 7 

